This invention relates to a process for testing the operating efficiency of exhaust gas catalysts inserted in the exhaust gas train of an internal-combustion engine.
A monitoring process is known from German Patent document DE-40 27 207 A. This monitoring process has several temperature sensors assigned to a catalyst. An average temperature value is formed from a long-term observation of measurable temperature variables and is compared with given limit values.
There is therefore needed a process for the testing of the operating efficiency of exhaust gas catalysts. The testing process must rapidly and reliably permit conclusions regarding the aging condition, that is, the conversion rate of the catalysts to be determined.
The present invention meets these needs by providing a process for testing the operating efficiency of exhaust gas catalysts inserted in the exhaust gas train of an internal-combustion engine. The internal-combustion engine is operated during a first time period. A first operating condition of the internal-combustion engine is determined by means of one or several parameters of the internal-combustion engine and/or the exhaust gas train which are sensed in an up-to-date manner and which are processed by a control unit and which, during this time period, must meet specified marginal conditions for the determination of this operating condition. The internal-combustion engine is operated during a second time period in the first operating condition if at least one of the sensed parameters corresponds to a specified desired value. Alternatively, a second operating condition of the internal-combustion engine is adjusted by changing the value of at least one of the sensed parameters of the internal-combustion engine. This second condition is recognized by the comparison of the up-to-date parameter value or values with specified desired values. The exhaust gas catalyst is acted upon by means of an exhaust gas pulse which does not correspond to the operating condition existing during the second time period. Values of at least one first parameter of the exhaust gas train which changes as a result of the exhaust gas pulse are sensed. At least one first parameter difference is formed from a parameter value sensed before or while the exhaust gas catalyst is acted upon by means of the exhaust gas pulse and its value after the exhaust gas catalyst is acted upon by means of the exhaust gas pulse. This first parameter difference is compared with a specified first desired difference range. The process is continued if this first parameter difference is within this desired difference range. The change of the first parameter is analyzed and a signal indicating the operational inefficiency of the exhaust gas catalyst is triggered if this change deviates from a desired change after one implementation or repeated implementations of the steps of this process. The operational inefficiency is stored in a fault memory of the control unit.
If the above process is used in the case of an internal-combustion engine, up-to-date information concerning the catalytic conversion rate of the exhaust gas catalyst may be obtained within a few seconds. The process can be carried out in different operating conditions of the internal-combustion engine or of a motor vehicle which is equipped with an internal-combustion engine; for example, in the idling operation, in the coasting operation, or in any partial-load operating point.
First, the internal-combustion engine is operated during a first time period, and a first operating condition is determined by an electronic control unit by means of parameters detected on an up-to-date basis. For this purpose, these parameters must meet certain marginal requirements during a specified lead time.
In this first operating condition, conditioned requirements of the internal-combustion engine and of the exhaust gas train exist so that there is sufficient reproduceability in the real driving operation. The parameters sensed in this case may, for example, be the engine load or rotational speed of the engine which, during the lead time, must comply with specific collective load and/or rotational-speed systems or with ranges or limit values.
After this first operating condition is determined, the internal-combustion engine continues to be operated in this first operating condition during a second time period if at least one of the sensed parameters corresponds to a specified desired value or, by means of the change of at least one value of a sensed parameter of the internal-combustion engine, a second operating condition is set, for example, by a change of the throttle valve angle to a coasting operation by the person operating the motor vehicle.
Furthermore, an idling operation, for example, may be set. This condition will subsequently be recognized by the comparison of the parameter value with the specified desired value. The second operating condition may also be any partial-load operating point in which the parameter corresponds to the desired value.
As a further step, in the second time period during the first operating condition, or after the recognition of the second operating condition, the exhaust gas catalyst is acted upon by an exhaust gas pulse of the internal-combustion engine which does not correspond to this condition. For example, in the idling operation, this pulse is generated by the fact that the injected fuel quantity of at least one cylinder of the internal-combustion engine does not correspond to the idling operation and a controlled under-stoichiometric or over-stoichiometric engine operation will therefore occur.
During coasting operation, in which the fuel supply is normally interrupted, the exhaust gas pulse can be generated, for example, by the injection of fuel into at least one cylinder, the ignition of which may be switched off for this purpose.
In an arbitrary partial-load point, the exhaust gas pulse may also be generated by one of the above-mentioned possibilities by means of the fuel quantity or the ignition.
The next step consists of the sensing of at least one first parameter in the exhaust gas train of the internal-combustion engine. This first parameter changes because of the exhaust gas pulse. This parameter may, for example, be at least one temperature sensed by a temperature sensor in front of, in, or behind the exhaust gas catalyst or catalysts. This temperature rises, for example, because of a short-term fuel rich driving operation. As an alternative in this respect, the concentration of a gas may be measured which is sensed by a gas probe, for example, the oxygen concentration by means of a lambda probe.
Before an analysis of the change of this first parameter value takes place, an abort criterion is checked as the next step. This avoids having an analysis takes place although, during the implementation of the process, certain parameters have changed on the basis of unpredicted events in such a manner that a reliable statement concerning the conversion rate would no longer be possible.
From at least one parameter value detected before, or while the exhaust gas catalyst is acted upon by the exhaust gas pulse, and from its value after the exhaust gas catalyst was acted upon, a first parameter difference is formed. This difference is compared with a specified first desired difference range. When, for example, during the coasting operation, the rotational speed changes in an unacceptable manner during this time period as a result of an abrupt braking, the process is terminated. If this parameter difference is within the desired difference range, an analysis of the first parameter will finally take place by means of the comparison of its change with a specified desired change.
After the above-mentioned process steps were again carried out or were carried out repeatedly, when there is an unacceptable deviation from the desired change, a signal is triggered which indicates the operating inefficiency of the exhaust gas catalyst. This signal is stored in the control unit and is displayed, for example, as a fault message in the dashboard of the motor vehicle.
The operating inefficiency is therefore not defined by the total failure of the conversion but by specific limit values.
In a particularly simple and space-saving manner, the analysis may take place by the comparison of the value of the first parameter sensed after the exhaust gas catalyst was acted upon with a specified stored desired value in that the change determined by means of this comparison is compared with a desired change range.
As a modification of the above, the analysis may take place by the direct measuring of the change of the value of the first parameter in that its value is, in addition, sensed during the second time period. A second parameter difference is formed from the two values and is compared with a specified stored second desired difference range.
The exhaust gas catalysts inserted in the exhaust gas train may be used as relatively large-volume main catalysts as well as comparatively small-volume starting catalysts.
The process according to the present invention requires only a few seconds to be implemented, so that disadvantageous effects of the exhaust gas pulse entered for a short time are not noticeable in the driving operation.
If the exhaust gas pulse is generated by an additional injection of fuel, the amount of fuel required for this purpose and the therefore emitted amount of exhaust gas are negligibly small.
By means of the adjustment of the marginal conditions, or of the desired changes in the control unit, an individual adaptation is possible to different internal-combustion engines, to different catalysts with their specific aging characteristics, as well as to tighter legal requirements or standards.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.